1. Field of Invention
The present invention relates to wireless communication between devices. In particular, the present invention is directed to coding techniques applicable to orthogonal frequency division multiplexing (OFDM) in wireless networking.
2. Description of Related Art
In recent years, there has been rapid growth in mobile computing and other wireless data services, as well as growth in fixed wireless access technologies. These services have the benefit of not requiring wiring between nodes to support the networking and potentially allow for communication where it could be difficult to provide a wired infrastructure. These services can be used to provide high quality telephony, high-speed Internet access, multimedia and other broadband services.
These services provide several challenges in the areas of efficient coding and modulation, quality improving signal processing techniques and techniques for sharing limited spectrum between users. One way to improve the capacity of wireless communication systems is to use multiple transmit and receive antennas. This is often achieved through coding techniques appropriate to multiple antennas, such as through space-time block-coding (STBC).
STBC is a coding technique used with multiple antennas to introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at a receiver, and coding gain when compared to an uncoded system, without sacrificing bandwidth. STBC helps increase reliability and can provide full diversity gains with simple linear processing of signals at a receiver.
The wireless channels used are subject to time-varying problems such as noise, interference and multipath issues. Additionally, for mobile systems, the communications should be accomplished through low power requirements so that the system can be simply powered and remain small and lightweight. This can often preclude signal processing techniques that can be used for reliable communications and efficient spectral utilization, if those techniques demand significant processing power.
As discussed above, when the resources of multiple antennas are available, the spatial domain can be utilized to achieve reliable transmission. In that case, some pairs of antennas are used for diversity gains and some groups used with multiplexing for higher throughputs. With these multiple streams, there is a need for interference cancellation at the receiver. However, the prior art does not provide such interference cancellation techniques for multiple streams. Additionally, because STBC is performed in the raw-data space, papers published never discuss coding/decoding techniques. However, if the noise in the signals is colored or is hard to estimate, it is not possible to provide soft decision processes in a Viterbi decoder. Thus, there is a need in the prior art for a means to estimate noise power in STBC, with or without multiplexing, and applicable to Viterbi decoding.